Photo timer



J. BALL ET AL June 18, 1957 A PHOTO TIMER 4 Sheets-Sheet 1 Filed Sept.9, 1954 ATTORMYS June 18, 1957 J. BALL-UAL PHOTO TIMER Filed Sept. 9,1954 4 Sheets-Sheet 2 PHG-3 INVENTORS JACK BALL 8 BY JOHN J. RUSSELLFIG-6 ATTORNEYS June 18, 1957 2,796,528

J. BALL ETAL PHOTO TIMER Filed Sept. 9, 1954 4 Sheets-Sheet 3 FIG-7FIG-8 Z l 6/ Eff HG ad 4'- s z o 2. r E' CENTER/.WE or zo/vE oFF CENTER0F .SCREEN INVENTORS.

JAcK BALL JOHH J. RUSSELL /N INCNES.

T/ME l deco/v0.5

June 18, 1957 J. BALL ET AL 2,796,528

PHOTO TIMER .Mex @ALL a BY Jamv J. eusse/.L

YTTOR/VEYS United Pnoro 'rnvmn This invention relates to improved meanssensitive to the luminosity of an image on a fluorescent screenv anduseful for controlling a timing period in a photographicV process.

This application is a continuation-in-part of our copending applicationSerial No. 116,112, led September 16, 1949, now abandoned.

An object of the present invention is to provide apparatus for use abovethe body of a patient being examined for timing an X-ray photograph of aselected portion of the patients anatomy. For this purpose a movable lmtray is positioned above the body of the patient with a fiuorescentscreen over the picture-taking position of the film in the tray and withthe upper surface of the screen at all times exposed to the clear visionof an operator standing by the patient. The X-ray tubek is positionedbelow the body of the patient with the rays directed upwardly throughthe body and impinging on the under side of the fluorescent screen inthe usual manner so that the X-ray image appears on the screen as itwill appear on an interposed film when a picture is to be taken. Ourinvention includes a photoelectric light-sensitive device secured to oneside of the screen in a low position to receive light rays from thescreen at a flat angle, the position of the light-sensitive device beingsuch that the upper surface of the screen is always clearly exposed tothe vision of the operator. It results from this arrangement that theoperator may view theV anatomy of the patient and select that portionwhich he desires to photograph, then center that selected portion sothat its image is in the center of the fluorescent screen, then move thelm tray to exposure position of the lm and time the X-ray photographutilizing the output of the photoelectric light-sensitive device toterminate the exposure with the assurance that he is getting that periodof exposure which will give him the best deiinition on the lm. Such aphotoelectric light-sensitive device may be used with or without acollimator but the device works better with a collimator so that thelight is transmitted to the photoelectric device more accurately limitedto a selected luminous area of the screen. While a single photoelectriclight-sensitive device positioned as herein described will operatefairly well, we find that two of these devices positioned on oppositesides of the fluorescent screen provide a more accurate timing means.

Another object of the present invention is to provide light-sensitivemeans subject to the luminosity eect of an image on a uorescent screenas observed from opposite sides thereof so as to average the lighteffects over a large portion of the entire image whereby a light area ofthe image which is nearer to one of the luminosity responsive deviceswill be farther away from the luminosity responsive device on theopposite side of the image, thus averaging the total light effect andobtaining a more accurate value for photographic timing purposes. In oneform of our invention, two photoelectric cells are positionedrespectively on opposite sides of the image 2,796,528 Patented June 18,1957 in position to receive light rays from a large area of the imageand theV electrical output of the two photoelectric cells is totalizedVor `averaged for timing purposes.

In another form of our invention, the luminosity eifect from theopposite sides of the image is focused by means of mirrorssimultaneously from two mirrors on to a single photoelectric cell, thusaveraging the light effect from opposite sides of the image in a singlecell, the output of which is utilized'in a timing circuit.

Another object of the present invention is to do away with the errorswhich occur by timing an X-ray photograph where the timing value isdetermined from one side only of the image.

Still another object of the present invention is to do away withcumbersome movable light-sensitive devices which have to be moved overthe image in the screen for operative purposes and thus are sensitive tothe particular spot on which the light-sensitive device happens to befocused and which is undesirable because ofY the wires connected to thedevice which have to be bent back and forth each time, together with theundesirability of having the vision of' the operator obstructed.

Other objects and advantages of our invention will beapparent from theaccompanying drawings and descriptionV and the essential features willbe summarized in the appended claims. v

In the drawings,

Fig. l'is a top plan view of a frame equipped with a fluorescent screenand a movable cassette or iilm holder and equipped with that form of ourdevice which requires two photoelectric cells;

Fig. 2 is a fragmental sectional View taken along the line 2-2 of Fig.l;

Fig. 3 is a fragmental sectional view enlarged taken Ialong the line3-.3 of Fig. 1 and partly broken away to more clearly show theconstruction;

Fig. 4 is a diagrammatic view of a portion of an electrical timingcircuit for use with the device of Figs. l, 2 and 3;

Fig. 5 is a top plan view of the left-hand portion of Fig. 1 to somewhatsmaller scale and showing a modified form of our device using mirrors;

Fig. 6 is a fragmental sectional View enlarged taken along the line 6 6of Fig. 5;

Fig. 7 is a diagrammatic view illustrating the position of the X-raytube, the body of the patient, the film and the iluorescent screen;

Fig. 8 is a graph showing the results obtained utilizingV one or twophotoelectric devices without a collimator;

Fig. 9 is a similar graph showing the results using one photoelectricdevice or two devices together with a collimator; while Fig. l() is adiagrammatic view of the uorescent screen and photoelectric devicesillustrating how the graphs of Figs. 8 and 9 were made.

Our invention is useful for photo-timing an X-ray photograph or fortiming an ordinary photograph of an X-ray image on a fluorescent screen.ln either case, the parts to be photographed are viewed as an image on afluorescent screen and some measure of the luminosity of the image mustbe utilized for timing purposes. One common device for photo-timing apicture under these conditions, consists in the use of a photo-sensitivetube which is moved to a central position of the picture when it isdesired to time an exposure. One of the diliiculties of this device isthat the photo-tube is in the way for viewing the screen whenV it ismoved to a position over the screen, and furthermore the device has highvoltage wires connected to it, which have to be bent back and forth eachtime the phototube is placed in position or pushed out of the way.Another didiculty with this type shadow such as the spine would make orover a brighter,

spot such as light tissue would make. This is particularly noticeablewhere a patient has been fed bismuth which, of course, provides a verydark spot, and if the phototube were placed over such a spot, a verydark picture would result.

Another manner of photo-timing such pictures is the provision of aphotoelectric tube or cell along one side of the fluorescent screen anddirected toward the image on the screen. T-his is a satisfactoryarrangement except that it does not average the lightV over the entirescreen, but has a greater effect from the areas lying close to thephototube rather than from the areas farther away. The eect of the lightof the image Yon thephototube follows the inverse square law andtherefore the image areas nearer to the phototube give a much greatereiect.

For instance, if it is desired to take a picture through one-half of thehuman body, if the phototube is toward the center of the body, then thedark portion of the body image will be nearer the phototube and theimage farther away from the phototube may have a certain amount ofsplash where the View extends outside the confines of the body itself,giving a very bright spot on the screen distant from the phototube andtherefore, the darker portion of the body nearer the phototube willcontrol and one will obtain a dark picture. On Vthe other hand, if thephototube is near one side of the body looking toward the center, thenany splash will be close to the phototube and the darker portion of thebody image will be farther away from the phototube. In this case, thetimer will cut oif the exposure tube quickly and a light print willdevelop.

Another manner of photo-timing an X-ray photograph is to. place theX-ray tube above the patient with the uoroscopic screen and ilrnbeneaththe patient. With this arrangement, the operator cannot move thefluorescent screen around and observe the image until he obtains theexact portion of the anatomy which he desires to photograph.

We have chosen to show our invention in combination with a frame whichcarries a fluorescent screen 11 in a binding frame 12 and mounted bymeans not shown for movement to various positions relative to the bodyof the patient to be observed. A cassette or lm tray 13 is mounted bymeans of rollers 14 for movement along parallel tracks 15 either to aphotographing position as shown in Fig. l or to a loading and unloadingposition in the area 16. For moving the tray 13 back and forth, a motor17 is provided which through a slip clutch connection 18 drives a pinion19 meshing with a rack 20 which in turn meshes with a mutilated gear 21formed on one end of an arm 22 which is oscillatable about a fixed pivot23 connected with the main frame 10. At the opposite end of lever 22 ithas a pivotal engagement with a shoe 24 which is slidable in a slottedframe 25 which is rigidly carried and is a part of the tray 13. Movementof the rack thus oscillates arm 22 to carry the tray 13 from loading tophotographic position and back again. The particular device shown in thedrawings is a'spot lm arrangement with stop members 26 and 27 carried byarm 28 which is pivotally mounted at 29 on the main frame and is movableby means of a handle not shown. A V-shape stop 30 adjustably mounted onthe tray 13 engages the stop 26 in the position shown in Fig. l so thatthe tray can move no farther toward the left. The slip clutcharrangeemnt 18 provides a safe manner of stopping at any desired point,the motor 17 being arranged to overdrive until a stop -member isreached. In this particular device, the tray 13 may be set to take apicture for each of its four quarters or for the left half or the righthalf or for the upper half or for the lower half or for the entire areaof the screen. The particular arrangement of the main frame 10 and themovements of the tray 13 have no special bearing on the presentinvention and are only shown to illustrate one embodiment thereof.

In the form of our invention shown in Figs. 1 to 4 inclusive, aphotoelectric cell 34 is mounted in xed position on the frame 10 at theleft-hand side of the lluorescent screen 11.

results are obtained with two cells, which is the preferred form of ourinvention. Preferably, therefore, a second photoelectric cell 34 ismounted in xed position on the frame 10 at the right-hand side of theuorescent screen as shown in Figs. 1 and 2. As shown in Fig. 2, thesephotoelectric cells extend a very short distance above the level of theframe, approximately one and one-half inches, so that they4 are entirelyout of the way and are not obstructing the view of the operator. Asclearly shown in Fig. 2, the angle A between the beam of light comingfrom the image on the fluorescent screen toward each of thephotoelectric cells is very dat, not substantially over ten degrees. Itresults from this construction that a Very shallow beam of depth B thusintercepts a Wide area of width C on the fluorescent screen. In otherwords, the light beams coming from the image toward each of thephotoelectric cells is derived from a very large area of the fluorescentscreen 11. Preferably, the openings to the photoelectric tubes areprovided with devices 32 for collimating the light entering the cellopenings. As shown in Fig. 3, this comprises a plurality of plates 33parallel to the axis of the photoelectric cell 34 or 34', and thisinsures that the beams of light directed to cells 34 and 34 come fromsubstantially the same exact area. In other words, the two beams overlapfor -the width of the image indicated at C in Figs. 1 and 2. 'I'he raysfrom each cell converge along the broken lines as shown in Fig. 1. Therays toward the cell 34 converge along the dot-dash lines D Vandconverge toward the cell 34' along the dot-dash lines E. Thus, exceptfor the outer corners as shown in Fig. l, the light beams moving towardcells 34 and 34'. come from substantially the same yarea of thefluorescent screen and come from quite a large area thereof so thatthere is no specialized effect from a particularly light or dark spot ofthe image on the screen. It will be obvious that a light spot of theimage nearer tube 34 will lhave a strong effect there but will have aweak effect on the tube 34. Thus, the luminosity elfects from oppositesides of the image are averaged.

An electrical connection between photoelectric cells 34 and 34 .so as toaverage out the results and to utilize this result in a timing circuitis illustrated in Fig. 4. The view of F-ig. 4 is intended to lbeincorporated in the timing circuit shown and claimed in the copendingapplication Serial No. 785,664 `of Jack Bal-l and Edward B. Graves forPhotoelectric Timer for X-Ray Apparatus, led November 13, 1947, newVPatent No. 2,541,137,

granted February 13, 1951, to which reference may be had fora morecomplete description. It will be noted that vthe, left-hand portion ofFig. 4 is exactly like asimilar part of the drawings in the abovementioned Patent No. 2,541,187 wherein a photoelectric `cell 34 is shownin a `broken line box indicated as 5S. The right-hand portion of Fig. 4is a complete duplication of the left-hand portionand 'any parts thereofmay be referred to with reference characters having the suffix prime Thephotoelectric tubes 34 and 34 are illustrated as being of the type shownin United States Patent No. 2,231,697 granted February 11, 1941, to V.K. Zworykin et al. The cathodes 34b and 34h' of the present applicationare intended to be the equivalent of the `cathode 5 of the abovementioned Zworykin et al. patent. It will be noted that whereas, in

the above mentioned Ball et al. patent, the termination of aphotographic exposure depends upon the tiring of the trigger tube 31responsive to the output from -a single A single photoelectric cell may,bek used for our purpose as hereinafter set forth, but bettery creasesphotoelectric cell 34, the timer circuit when connected according to theteachings of Fig. 4 and the above mentioned Ball et al. patent connectsYin parallel the plates 34a and 34a of the two phototubes by means ofthe connector 57. It is well known to iire a trigger tube when aconnected condenser has collected suicient electrons from an anode suchas 34a of cell 34. The presen-t invention supplies means for chargingsuch a condenser 56 responsive to the average luminosity ofsubstantially the entire screen by connecting anodes 34a and 34a inparallel.

A trigger tube 31 -is shown as of the cold cathode tube. The plate 31aof this tube is connected through relay 32 having an armature 32a thepurpose of which is to open a set of contacts and terminate the X-rayexposure responsive to the timing apparatus herein disclosed.

A phototube of the above mentioned Zworykin type is diagrammaticallyshown at 34. This tube has a plate 34a, a cathode 34b and a plurality ofdynodes. Suitable taps on resistor 44 supply the dynodes with propervoltage all except the ylast one. This last dynode is connected toswitch 52, which, in the full line position shown in the drawings,engages contact 52a for radiography. The series resistor 46 is used as acalibrator. The phototube units are sent out fully assembled includingthe parts within the broken line 55. By adjusting the resistor 46, eachphototube unit may be adjusted to the same sensitivity so as to giveidentical output.

A capacitor 56 is provided for collecting the electrons from the anode34a of the phototube until a suticien-t charge is collected to tire thetrigger Itube 51. This condenser is connected with Iline 57 which inlturn connects the anode 34a of the phototube with the cathode of thetrigger tube. The other side of the condenser is grounded through line58. The capacitor 56 is normally short-circuited through line 59 andswitch 20c until an exposure starts. At that time, the switch 29C opensand the capacitor begins yto collect a charge. By proper selection ofthe capacity of the capacitor 56, the potential to which it is chargedin order `to iire the trigger tube, and the ensitivity of the phototube,an exposure may be terminated when a recording film has been properlyexposed. The capacitor 56 and the trigger tube 3l are so selected andarranged as lto take care of the output from the two photoelectric cells34. and 34 as here shown, or from one cell if connected as in Patent No.2,541,187, so as to terminate the X-ray exposure after the lm has beenproperly exposed.

Certain refinements will occur to those skilled in this art in order tomake the above device 4operate properly. In the rst place, each of thecells 34 and 34 will be separately focused on the same a-rea, lighted inthe 4same manner, and each of the phototube units will be adjusted tothe same sensitivity so as to give identical output for identical input.This is done "by adjusting the resistor 46 for cell 34 and by adjustingthe equivalent resistor for the cell 34'.

The apparatus mentioned -so far utilizes two photoelectric cells andtotalizes the output of the two cells electrically in order to obtain`an average result from the image on the fluorescent screen. Themodification shown in Figs. and 6 averages the luminosity etiectobserved from each side of `the image by simply adding together thelight rays as they effect a single photoerectric cell. All of the partsof Fig. 5 are understood to be the same as those described in connectionwith Fig. l except those now about to be described. Positioned in fixedrelationship to the trame 19 on opposite sides of the fluorescent screenil, We provide housings 35 and 37. In each of these housings there is amirror 3S so positioned as to receive light rays from the image on theiiuorescent screen and to reflect these rays parallel to thedot-dot-dash lines F of Fig. 5 to the cathode 39 of a photoelectric cell46 which is mounted on the frame 1i?. The cathode 39 is of a similarcharacter to that previously described at 3411 gud 34h'. Collimatingdevices 41 exactly equivalent to the devices 32 are positioned in frontof each of the mirrors 38 to provide parallel rays of light coming fromthe uorescent screen toward each mirror and limiting the area covered bythe rays of light going in opposite `directions to the same width ofimage as indicated at C in Figs. l and 2 in connection with the tirstform of our device. If necessary or desirable, a lens 42 may bepositioned between each device 41 and the associated mirror 38 so as toconverge all `of the stray rays of light onto the mirror 38.

The operation of the device of Figs. 5 and 6 should now be apparent. Thephototube 40 takes the position of the photoelectric cell 34 as shown inthe above mentioned Ballet al. patent. The cathode 39 takes the place ofthe cathode 34b of the Ball et al. patent. The output equivalent to 34aof the photoelectric cell 40 is directed to a trigger tube such as shownat 31 in the Ball et al. patent to produce a timing operation. Thenecessary corrections can be -made to take care of the light coming fromtwo sources toward the cathode 39 in the present instance, but it willbe obvious to those skilled in this art how this may be done so as toutilize the photo-timing circuit of the Ball et al. patent. J

Referring to Fig. 7, a preferred arrangement of our device is shownwherein an X-ray tube 6 is positioned beneath a table 7 upon which thebody 8 of a patient lies. The iilm tray 10a is movably positioned overthe patient -in the usual manner With the tluorescent screen 11 over thepicture-taking position of the film 9 which is movable in the tray aspreviously described. A single Photoelectric cell 34a may be positionedas shown in Fig. 7 or two cells 34 and 34 may be positioned on the trayas illustrated in Figs. l and 2.

It is obvious that the arrangement diagrammatically illustrated in Fig.7 has great advantages from the point of View of the medicalpractitioner or operator utilizing the device. Using tiuoroscopy, theoperator moves the tray 16a to a position where the uorescent screen 11is over the body of the patient 8. The X-rays cause the usual image ofthe body parts to appear on the screen 11 and the operator may selectthat portion which he desires to photograph very accurately in themiddle portion of the screen li. He will then slide the iilm 9 from theloading position indicated at 16 in Fig. l to the position beneath thescreen il as indicated in Fig. 7, it being understood that the X-raytube is meanwhile deenergized. The tube is then energized to take aphotograph making use of a timer such as We have herein described underthe control of a single phototube 34a or a pair of phototubes 34 and 34.This arrangement has great advantages for taking a selected picture atthe right exposure and is better than any previously known arrangementto the best of our knowledge.

In order to investigate the etectiveness of one or two photoelectricdevices with or without collimators, We set up a device asdiagramrnatically illustrated in Fig. 10. The lluorescent screen 11 wasset up to receive an image as illustrated in Fig. 7. Photoelectric cellsX and Y were set up on opposite sides of the uorescent screen as taughthereinabove and arranged so that one or both of these cells could beutilized for timing purposes as hereinabove described. All of the screen1i was blocked oi so far as visible light was concerned by means of tapeor ber board leaving exposed only a one inch strip as indicated betweenthe broken lines 5 of Fig. l0. The light sensitive devices X and Y werefocused primarily upon a space 4 inches by 4 inches square in the middleof the screen 11.

Referring now to Fig. 8, with the open strip 5 of Fig. 1G positionedcentrally on the center line 4, that is, With one-hait inch of the openstrip on each side of the center line, with a given image and a givensetting of all of the values in the control circuit shown in Fig. 4, thetimer was tripped at approximately 0.55 second and this is the pointplotted on line 60 of Fig. 8 at the abscissa marked` zero whichcorresponds to the center line 4 of Fig. 10. For the curve 60 only thephotocell X was utilized Without any collimator. A series of suchexposures was made leaving the exposedV strip 5 of Fig. 10 in variouspositions to the left and right of the center line 4 of Fig. 10, thenumber of inches being indicated `as ordinates in Fig. 8. For instance,with the'centerof strip 5 two inches to the left of the center line, atiming period of approximately 0.35 second was obtained which is alsoplotted on curve 6i). On the other hand, when the strip 5 was centeredtwo inches to the right of the center line (on the side away from thephotocell X) the timer was tripped at about 1.05 seconds which appearsat the ordinate 2 at the right-hand side of the ordinate 0 in Fig. 8. Ata position four inches to the left of the center line the timinginterval became 5.25 seconds and at four inches toward the right of thecenter line, the timing period became approximately 3.0 seconds asplotted on the curve 60 of Fig. 8.

Utilizing two photocells X and Y, the experiments wererepeated movingthe open strip 5 of Fig. 10 to various positions on each side of thecenter line 4 and plotting the timing periods as abscissa on curve 61 ofFig. 8 at various positions on opposite sides of the center lineindicated at zero. It will be seen that this gave a fairly flat curvebetween 2 inches to the left and 2 inches to the right of center ascompared to the same portion of curve 60 which sloped upwardly towardthe right. It is assumed that an ideal curve would be approximately likethat shown in dot-dash line at 62 in Fig. 8 where the timing periodwould remain constant over the 4 inch distance desired from 2 inches tothe left of center line to 2 inches to the right thereof, and on eitherside thereof the timing would go to infinity. It will be seen that thetwo photocells working together producing curve 61 of Fig. 8 come closerto producing this ideal response than does the single phototube X, theresults of which are plotted on curve 60.

The same experiments were repeated with a collimator in each of thephotocells X and Y and the results are plotted in Fig. 9. Curve 63 ofFig. 9 shows the results using a single phototube X with a collimator asillustrated in Fig. 3 and curve 64 are a similar set of experimentsmoving the open strip 5 as previously described to left and right of thecenter line indicated at zero. In this case each of the cells X and Yhad a collimator similar to that shown in Fig. 3. The ideal type ofcurve is again indicated at 65 in dot-dash lines.

Comparing Fig. 9 with Fig. 8, it will be seen that the collimator moreclosely restricts the field observed by the photocell so that the curves63 and 64 curve upwardly more sharply on each side of the center line,and the curve 64 more closely approximates the ideal type of curve 65than any other combination which we have tried.

What we claim is:

l. In X-ray apparatus involving a planar fluorescent screen havingthereon an image of unevenly distributed luminosity, the combinationtherewith of two devices positioned so as to be responsive to theluminosity of substantially the same area of said screen, said devicesbeing located on opposite sides of said image and sufciently adjacentthe plane of said iluorescent screen so that the light rays from saidimage approach said devices at a flat angle not substantially over tendegrees,

and photoelectric cell means operatively associated with both of saiddevices connected to average the luminosity elects from said twodevices.

'2. The combination of claim 1 wherein said devices comprise/twophotoelectric cell'sY positioned respectively on opposite sides of`saidimage, anda timing circuit connecting the output of said photoelectriccell means in parallel.V

3. The combination of claim l wherein said devices comprise two mirrorspositioned respectively on opposite sides of said image at an angle toreceive light rays therefrom, and said photoelectric cell meanscomprises a single photoelectric cell having a cathode positioned toreceive light rays simutaneously from both of said mirrors, and a timingcircuit responsive to the electrical output of said cell.

4. Apparatus for use above the body of a patient being examined fortiming an X-ray photograph of a selected portion of the patients anatomyand comprising a movable lm tray having a fluorescent screen over thepicture-taking position of said film in said tray and with the uppersurface of said 'screen exposed to the vision of an operator standing bythe patient, an X-ray tube below the body with its rays directedupwardly whereby the X-ray image appears on said screen as it willappear on an interposed lm, a photoelectric light-sensitive deviceoperatively connected with said screen at one side thereof and inposition to receive light rays from 'said screen at a flat angle notsubstantially greater than ten degrees, said device positioned to leavethe upper surface of said screen exposed, a Vcollimator positionedbetween said device and said screen arranged to collimate the lighttransmitted to said device to thereby more accurately |limit theluminous area of the screen from which light rays impinge on saiddevice, X-ray exposure time terminating means, and the electrical outputof said device operatively connected with said time terminating means.

5. Apparatus for use above the body of a patient being examined fortiming an X-ray photograph of a selected portion of the patients anatomyand comprising a movable ilm tray having a fluorescent screen over thepicture-taking position of said lm in said tray and with the uppersurface of Isaid screen exposed to the vision of an operator standing bythe patient, an X-ray tube below the body with its rays directedupwardly whereby the X-ray image appears on said screen as it willappear on an .interposed film, a photoelectric light-sensitive deviceoperatively connected with said screen at one side thereof and inposition to receive light rays from said screen at a at angle notsubstantially greater than ten degrees, said device positioned to leavethe upper surface of said screen exposed, X-ray exposure timeterminating means, and the electrical output of said device operativelyconnected with said time terminating means.

6. The combination of claim 4 including two of saidY [photoelectriclight-'sensitive devices positioned on opposite sides of said uorescentscreen, and the electricail outputs of said devices connected inparallel circuit with said time terminating means.

UNITED STATES PATENTS References Cited in the le of this patent2,486,866 Morgan et al Nov. l, 1949 2,666,145 Eversole et al. Ian. l2,1954 2,668,913 Goldeld et al; Feb. 9, 1954

